Various devices have been proposed for implantation in the human body for opening and closing the urethra when the sphincter muscle is unable to perform this function. Some of such devices are shown in U.S. Pat. Nos. 3,744,063, 3,863,622, 3,854,469, 3,903,894, and 4,019,499. They include a resilient inflatable cuff or other member that is implanted to surround the urethra and which when inflated by a fluid squeezes the urethra closed and when deflated permits the urethra to open.
In one such prior device as yet unpublished there is a bulb of flexible material that comprises a reservoir for the fluid and a valved control unit to control flow of fluid in both directions between the cuff and reservoir. The control unit includes a spring seated valve element that may be unseated by an abutment through manual operations to permit flow of fluid from the cuff to the reservoir and wherein the valve seat is movable by pressure of fluid within the reservoir to a position away from the valve element when the valve element is against the abutment to permit flow of fluid to the cuff. The valve element is also unseatable by excess fluid pressure in the cuff to thus act as a pressure relief valve. However, the arrangement is such that the spring force for seating the valve element is gradually overcome by the increasing differential in fluid pressure between the cuff and reservoir so that there is a diminishing seating force on the valve element as the relief pressure is approached. This results in less assurance that the valve will remain closed prior to the time that excess pressure in the cuff is experienced and hence leakage across the valve and opening of the urethra may occur at inconvenient times.